Re: [SI-LIST] : 20H Revisited

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From: Sainath Nimmagadda (sainath@lsil.com)
Date: Thu Jan 13 2000 - 16:19:16 PST


Michael, I don't see any contradiction. Consider the underlying theory as the coin and the disciplines as the sides. Of course, the two sides appear different for
normal coins. I believe system/signal integrity gets better as we begin to appreciate the unity in the diversity of various disciplines. On the other side of the
coin, we need diversity in disciplines for technology growth and, as you mentioned, steady paychecks. Oops! did I spin the coin again?

Sainath

Michael Vrbanac wrote:

> Sainaith,
>
> Thanks! Perhaps I should have originally said... "it was a 'non-SI' issue" to
> be more technically correct and be better understood.
>
> I hate to be a bit contrarian here but I don't think they are" two sides of the
> same coin". The underlying theory is the same but the "disciplines" aren't.
> I think there might be a bunch of folks who haven't yet figured that out. I'll
> bet you know of some brilliant SI folks who would not enjoy working with
> EMC for instance. They'd be out of their league. I believe there is a reason
> for this.
>
> Electromagnetics and field theory are the general labels for all the underlying
> physics for what we do. EMC would be a bit more specific to better define
> the specific use of electromagnetics and field theory to make an electrical
> device not only compatible with its environment but also with itself so that
> proper operation can be insured for the subject machine and all those in its
> environment. SI is even more defined and a subset of that. It is the use of
> electromagnetics and field theory to insure that the subject machine can
> properly operate and deal with its own internal issues. It is usually involving
> basic functional and reliability issues and essentially works with signal levels,
> thresholds, and purity as a specialty. Maybe that's not the best definitions
> but at least its a first cut at it. (BTW, there's always room for some exceptions.)
>
> When one considers the "language" of SI and the "language" of EMC and also
> the views, focus, and goals along with that, we find that they are different things.
> Even the simulation tools for the two are different. I have managed a group that
> did both EMC and SI so I know. People can bridge that distinction as I have
> but make no mistake. They aren't the same thing. Related in some ways but
> not the same.
>
> Michael E. Vrbanac
>
> Sainath Nimmagadda wrote:
>
> > Thank you Ray and Michael, for quickly picking up my comment and clarifying. For people who do not know that fields and SI are two sides of the same coin, I was
> > afraid Michael's 'side note' might mislead them that they are not related subjects. Hence the comment.
> >
> > Sainath
> >
> > Michael Vrbanac wrote:
> >
> > > Sainath,
> > >
> > > Everything to do with SI is ultimately a field problem. (T-line work & crosstalk, are
> > > easy examples.) It isn't always convenient to handle SI that way, though. Let me
> > > explain.
> > >
> > > Most engineers aren't specialists in field issues although they may know something
> > > about them. Since most of the issues SI folks deal with appear in the time domain,
> > > many times it is easier to stay in that domain (i.e. keep the problem as simple as
> > > possible and still get the job done!) Also, SI folks need to speak the "language"
> > > of the design engineer who is working in the time domain.
> > >
> > > The field simulators that we use for SI are designed to relieve us from having to
> > > directly deal with field theory and make our jobs much easier (thank goodness!).
> > > The "bad news" is that we might begin to lose touch with our field theory skills
> > > because the simulator is supposed to do that for us (and that can create even
> > > larger issues.) The "good news" is, in the near term, we become more effective
> > > in producing meaningful results which, of course, results in products entering the
> > > market which then translates into a steady paycheck for the SI engineer!
> > >
> > > Michael E. Vrbanac
> > >
> > > Sainath Nimmagadda wrote:
> > >
> > > > Interesting! What SI issues have to do with fields anyway.
> > > >
> > > > Sainath
> > > >
> > > > Michael Vrbanac wrote:
> > > >
> > > > > D.C.
> > > > >
> > > > > re: change in orientation of the fringing fields
> > > > > Yes. That's a very good point.
> > > > >
> > > > > re: Vss plane being cut back instead
> > > > > In the original application of the 20H rule, it probably wouldn't have mattered.
> > > > > In later applications (and alterations) other than the original, it might have mattered.
> > > > >
> > > > > As as side note:
> > > > > The original 20H rule came out of a "field" problem being solved. From
> > > > > that standpoint, it might have actually been true to some extent to have
> > > > > called it a "screwy SI rule" because it really wasn't an SI problem to begin
> > > > > with. Knowledgeable folks dealing with SI issues would never have
> > > > > classified the original use as an SI issue. Subsequent uses of the 20H rule
> > > > > may indeed have blurred the lines a bit.
> > > > >
> > > > > Michael E. Vrbanac
> > > > >
> > > > > "D. C. Sessions" wrote:
> > > > >
> > > > > > Keeping in mind that There Is No Ground, what happens if
> > > > > > the Vss plane is the one cut back?
> > > > > >
> > > > > > As an alternate consideration, note that the stepback would
> > > > > > change the orientation of the fringing fields, which would
> > > > > > interact with the enclosure to potentially limit net radiation.
> > > > > >
> > > > > > --
> > > > > > D. C. Sessions
> > > > > > dc.sessions@vlsi.com
> > > > > >
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